Chinese authorities have seized assets worth at least 90 billion yuan (S$18 billion) from family members and associates of retired domestic security tsar Zhou Yongkang, who is at the centre of China's biggest corruption scandal in more than six decades, two sources said. -- FILE PHOTO: REUTERS

BEIJING (REUTERS) - Chinese authorities have seized assets worth at least 90 billion yuan (S$18 billion) from family members and associates of retired domestic security tsar Zhou Yongkang, who is at the centre of China's biggest corruption scandal in more than six decades, two sources said.

More than 300 of Zhou's relatives, political allies, proteges and staff have also been taken into custody or questioned in the past four months, the sources, who have been briefed on the investigation, told Reuters.

The sheer size of the asset seizures and the scale of the investigations into the people around Zhou - both unreported until now - make the corruption probe unprecedented in modern China and would appear to show that President Xi Jinping is tackling graft at the highest levels.

But it may also be driven partly by political payback after Zhou angered leaders such as Mr Xi by opposing the ouster of former high-flying politician Bo Xilai, who was jailed for life in September for corruption and abuse of power.